Conventionally, as a spindle apparatus of a machine tool or the like, a built-in motor spindle apparatus having a front side bearing interposed between a front housing and a spindle shaft and a rear side bearing interposed on an outer periphery of a rear portion of the spindle shaft is conventionally known, as described in, for example, JP-A-7-112303 (hereafter referred to as a “patent document 1”) and JP-A-2003-159622 (hereafter referred to as a “patent document 2”).
As shown in FIG. 31, a built-in motor spindle apparatus 500 disclosed in the patent documents 1 and 2 includes a motor housing 502 held by a unit supporting member 501, as well as a front housing 503 which is joined to a front side of this motor housing 502. The built-in motor spindle apparatus 500 further includes a spindle shaft 505, which is fitted in this motor housing 502 and the front housing 503, and a stator 506 secured to an inner periphery of an intermediate portion of the motor housing 502, a rotor 507 being secured to an outer periphery of the intermediate portion of the motor housing 502.
Further, the spindle shaft 505 is formed in a hollow tubular shape, and a drawbar 509 which is urged by a coned disk spring 508 and is slidable in the tube is provided in the tube, a chuck portion 510 being provided at its tip. Further, four front side bearings 511 are interposed between the front housing 503 and the spindle shaft 505. In addition, a rear side bearing 512, which is a cylindrical roller bearing, and a bearing sleeve 513 are fitted over an outer periphery of a rear portion of the spindle shaft 505, and a rear cover 514 is bolted to a rear portion of the motor housing 502.
Incidentally, with the machine tool, a failure of the spindle is frequently caused primarily by damage occurring in the bearings. Its causes are the life of the bearings, a collision of the spindle due to a machining program error, and the like. The reduction of the time (downtime) from the failure of the spindle until it is reset is particularly important at a site of parts machining which is directly linked to a production line of automotive parts machining or the like. In addition, a trend toward the higher speed of the machine tool spindle is under way, and the spindle bearing life for low-speed machines (less than 600,000 dmN) (dm: pitch circle diameter (mm) of a rolling bearing, N: rotational speed (min−1)) has been virtually unlimited at 100,000 hours or more, whereas the spindle bearing life for high-speed machines is becoming 10,000 to 20,000 hours. Thus, the spindle bearings have come to be regarded as being handled as consumables, so that there has arisen a need to lower the maintenance cost.
With the spindle apparatus 500 disclosed in the above-described patent document 1, the spindle shaft 505 is arranged to be drawn out for the improvement of the maintenance efficiency. However, with this arrangement, although the spindle shaft 505 can be drawn out, no description is given as to the replacement of the rear side bearing 512 which is a cylindrical roller bearing. If the rear side bearing 512 is damaged, the time and trouble involved in the maintenance remain unchanged from a conventional case. In addition, since a projecting portion of a lubricating nozzle is not provided to draw out the spindle shaft 505, 2 to 10 hours or thereabouts is inevitably required as the running-in time for the rear side bearing 512 after its assembly. Hence, there has been a problem in that the downtime becomes long.
In addition, with the spindle apparatus 500 disclosed in the above-described patent document 2, there has been a problem in that the operating efficiency is poor, since at the time of removing the spindle, an operator must move around to the rear side to remove a pipe, and at the time of assembly an operation is further required for adjusting a bearing case to the phase of the pipe.
As another example of the spindle apparatus of a machine tool or the like, a spindle apparatus in which a plurality of coned disk springs are stacked and disposed between the sleeve housing and the bearing sleeve is conventionally known, as described in, for example, JP-A-11-138305 (hereafter referred to as a “patent document 3”).
In the spindle apparatus, one bearing (rear side bearing) is fixed to the bearing sleeve which is fitted in the sleeve housing and is movable in the axial direction, so as to be able to absorb the axial displacement when the rotating shaft has become axially elongated due to heat generation or the like at the time of high-speed rotation. As for the fit between the sleeve housing and the bearing sleeve, a plane surface sliding method in which a simple fit is used, a ball sliding method using an axially movable ball bush, and the like are known. Slidability as well as radial stiffness and axial vibration damping properties are required for the bearing sleeve for supporting the free end side of the rotating shaft.
In the case where the plane surface sliding method is adopted for the fitting between the sleeve housing and the bearing sleeve, the fitting clearance decreases in conjunction with heat generation, so that it is necessary to set an initial fitting clearance to be large. This has constituted one factor increasing the vibration of the rotating shaft when the spindle apparatus rotates. Meanwhile, in the case of the ball sliding method of the fitting using the ball bush, an increase in the interference due to heat generation hinders the smooth axial movement of the bearing sleeve, and the axial stiffness is low. Hence, there have been cases where self-excited vibration called the chattering of the rotating shaft occurs.
For this reason, in the spindle apparatus disclosed in the patent document 3, to damp the self-excited vibration of the rotating shaft, the arrangement is provided such that a plurality of coned disk springs are stacked between the sleeve housing and the bearing sleeve so as to increase the axial stiffness and prevent the self-excited vibration through the friction of the coned disk springs.
However, in the spindle apparatus disclosed in the patent document 3, the self-excited vibration is arranged to be damped through the friction of the coned disk springs, and the damping force is determined by the spring constant of the coned disk spring, the number of the coned disk springs, their installation direction, and the like. These items, which are set at the time of assembling the spindle apparatus, are constant and fixed unless the coned disk springs are recombined by such as disassembling the spindle apparatus. In other words, it has been difficult to change the characteristics in correspondence with the conditions of rotation, e.g., to reset the damping factor and the like to values optimal to the operating conditions.
In recent years, the trend toward the higher speed of the spindle apparatus is noticeable, and the amount of heat generated has also increased in consequence of the trend toward the higher speed. Therefore, there has been a demand for a more sophisticated method of supporting the rotating shaft, which is capable of coping with it.
In addition, as one example of the machine tool having the spindle apparatus, a machine tool in which the housing of the spindle head is divided into a front housing and a rear housing and the two members are fastened by bolts is conventionally known, as described in, for example, JP-A-2003-159622 (the “patent document 2”).
In such a machine tool, an arrangement is provided such that not the entire cartridge but the shaft, the front side bearing, the front housing, the rotor of the built-in motor, the rear side bearing, and the rear housing are removed as a spindle sub-assembly by leaving the stator of the built-in motor and the outer cylinder.
Incidentally, in a machine tool, in a case where the spindle apparatus is replaced due to a failure or the arrival of its life, with a type which is so constructed as to incorporate the bearings and the stator individually into the spindle head, the replacement operation takes time, and the downtime of the machine increases. Accordingly, it is known that the replacement time can be shorted by structuring the spindle apparatus so as to be capable of being divided and assembled integrally as a cartridge with respect to the spindle head.
Although there is also a type having a structure in which the entire spindle cartridge is drawn out, with this structure it is necessary to disengage oil and air pressure pipings and cables in the case of the built-in motor system, so that the operation takes time.
In contrast, in the above-described patent document 2, the arrangement is provided such that not the entire cartridge but the shaft, the front side bearing, the front housing, the rotor of the built-in motor, the rear side bearing, and the rear housing are removed integrally as a spindle sub-assembly by leaving the stator of the built-in motor and the outer cylinder. However, although at the time of disassembling the spindle cartridge it is necessary to withdraw from the spindle head all the portion of the spindle cartridge which is located inside the spindle head, the spindle cartridge is a heavy piece and cannot be pulled out manually.
Accordingly, the spindle cartridge can be drawn out safely and in a short time if the spindle cartridge is fixed to a worktable of the machine tool and is drawn out by making use of the feeding in a Z-axis which is a feeding axis parallel to the axial direction of the spindle. However, if the amount of Z-axis movement is shorter than the length necessary for the spindle cartridge to be completely drawn out from the spindle head, the withdrawal making use of the Z-axis feeding becomes impossible.
In addition, when the spindle cartridge is disassembled, the operation of disengaging many oil and air pressure pipings and cables is required, and the replacement time is long. In contrast, in the case of the spindle sub-cartridge, the operation of disengaging the many oil and air pressure pipings and cables is not required. However, if the amount of Z-axis movement is shorter than the length necessary for the spindle cartridge to be completely drawn out from the spindle head, the withdrawal making use of the Z-axis feeding becomes similarly impossible.
Meanwhile, in the case of a structure in which a flat mounting surface is provided on a side surface of the spindle cartridge and the spindle cartridge is fixed from its side surface to the spindle head, the spindle cartridge can be disassembled from the spindle head irrespective of the amount of Z-axis movement. With this method, however, since the load is received only by the side surface of the spindle cartridge, the fastening stiffness becomes low, so that this method is inappropriate in terms of stiffness.
In addition, with the above-described patent document 2, it is unnecessary to disengage the oil and air pressure pipings and cables, but parts cannot be removed excluding those parts which can be removed as a sub-cartridge. For this reason, this arrangement does not function effectively at the time of the failure of the stator, an unclamp cylinder, or the like, so that this arrangement lacks a functional feature concerning disassembly.
The spindle apparatus and the machine tool having the spindle apparatus in accordance with the invention are invented in view of such circumstances, and a first object of the invention is to provide a spindle apparatus which facilitates assembling and removing operations at the time of maintenance and which is low cost. A second object of the invention is to provide a spindle apparatus which has high stiffness and excels in satisfactory damping properties and slidability. A third object of the invention is to provide a machine tool in which a spindle cartridge or a spindle sub-cartridge can be disassembled and assembled in a short time, which minimizes the machine height, and which has high stiffness. A fourth object of the invention is to provide a spindle apparatus which is capable of attaining improvement of the maintenance efficiency by making it possible to facilitate the operation of replacing all internal component parts.